The present invention relates to a fuel vapor treatment apparatus (hereinafter referred to as a canister) for absorbing the fuel vapor emanating from the fuel reservoir chamber of a vehicle such as a fuel tank so as to limit gasoline vapor discharge into the atmosphere.
A conventional canister of the above-described type is disclosed in Japanese Unexamined Utility Model Publication No. 53-162214. In this canister, the fuel vapor from the fuel tank of a vehicle is introduced through a conduit into the upper portion of an absorbent layer incorporated in the cansiter so as to be adsorbed by the absorbent layer.
Such a conventional canister has adsorption characteristics such as those shown in FIG. 12. FIG. 12 shows the relationship between the L/D and the amount of fuel vapor adsorbed by the canister which was obtained by the present inventors through experiments, where L is the height of the canister, and D is the diameter thereof. As is clear from the graph, a canister arranged with L/D&gt;1 has an excellent adsorption efficiency.
However, this setting applies only to a canister which collects the fuel vapor that flows thereinto at a low flow rate, such as that vapor emanating from the fuel stored in a fuel tank or that rising from a float chamber provided in the carburetor of a vehicle. In the case of a large volume of fuel vapor which flows into the canister at a high flow rate, the above-described setting is not effective in increasing the adsorption efficiency. FIG. 13 shows the relationship between the L/D and the amount of fuel vapor absorbed which was obtained by the present inventors through experiments. In these experiments, the fuel vapor flowed into the canister at a flow rate of 30 to 40 l/min. This means that the size of the canister has to be increased in order to provide a sufficiently high adsorption efficiency. This causes a problem involving the mounting of the canister on the vehicle.